In recent years, a polymerizable liquid crystal compound is utilized in an optically anisotropic article, such as a polarizing plate and a phase retarder. This is because the compound exhibits optical anisotropy in a liquid crystal state, and the anisotropy is fixed through polymerization. The optical characteristics that are required for a molded article having optical anisotropy vary depending on purpose, and such a compound is necessary that has characteristics conforming to the purpose. For the compound used in the purpose, characteristics relating to the polymer are also important in addition to the aforementioned anisotropy. The characteristics include polymerization rate, and transparency, mechanical strength, coating property, solubility, crystallization degree, contracting property, water permeability, water absorbency, melting point, glass transition point, clearing point, chemical resistance and the like of the polymer.
Among the polymerizable liquid crystal compounds, a compound having an acryloyloxy group as a polymerizable group has high polymerization reactivity and provides a polymer having high transparency, and thus used widely for the purpose (Patent Documents 1 to 3). A polymerizable liquid crystal compound may be used solely or as a composition with plural compounds mixed. It may also be used as an ink with an organic solvent added thereto for controlling coating property. For producing a film having optical anisotropy by using the polymerizable liquid crystal compound (composition), an ink having been controlled in solution viscosity, leveling property and the like is prepared by dissolving the polymerizable liquid crystal compound (composition), a photopolymerization initiator, a surfactant and the like in an organic solvent. The ink is coated on a transparent substrate film having been subjected to an orientation treatment, and the solvent is dried to orient the polymerizable liquid crystal compound (composition) on the substrate film. It is then polymerized by irradiation with an ultraviolet ray to fix the orientation state. As the organic solvent, an ordinary solvent, such as a hydrocarbon solvent, e.g., toluene, and a ketone solvent, e.g., methyl ethyl ketone and cyclopentanone, is used, but according to the recent issues on environmental load, safety (mutagenicity and toxicity) and the like, there is a demand of use of an organic solvent having high safety, such as propylene glycol monoethyl ether acetate (PGMEA), with low environmental load. However, the polymerizable liquid crystal compounds in Patent Documents 1 to 3 have low solubility in the organic solvent having high safety, and have a problem of failure in preparation of an ink having a sufficient concentration (20% by weight or more). The failure in preparation of an ink having a sufficient concentration prevents a coated film having a sufficient thickness upon coating, and as a result, such a film cannot be produced that has intended optical anisotropy. The inventors have developed a polymerizable liquid crystal compound having a fluorenone skeleton (Patent Document 4). However, the compound is poor in a solvent, such as PGMEA, to fail to provide an ink having a high concentration. Furthermore, it has a high melting point and thus has such a defect that when the compound is liable to form crystals deposited when it is once heated to form a liquid crystal and then allowed to stand at room temperature.
Patent Document 1: JP-A-7-17910
Patent Document 2: JP-A-8-3111
Patent Document 3: JP-A-9-316032
Patent Document 4: U.S. Pat. No. 6,824,709